This invention relates generally to digital communication channels for local area networks and, more particularly, to techniques for using unshielded twisted pairs of conductors as a communication medium in a high-speed local area network. High-performance local area networks (LANs) typically use optical fiber or coaxial cable as the communication medium. For example one token ring network using optical fiber is known as the fiber distributed data interface (FDDI), and is intended for operation at a bandwidth of 125 megabits per second (Mb/s) over distances of about two kilometers. The physical layer medium dependent (PMD) sublayer protocol for FDDI is defined in an American National Standards Institute (ANSI) document designated X3T9.5/84-88. The other sublayer of the physical layer is known as the physical layer protocol (PHY) and is defined in ANSI X3.148-1988.
A significant drawback to LANs using optical fiber as the communication medium is the relatively high cost of the optical fiber. Relatively slow LANs have been proposed using much cheaper unshielded twisted pair wiring, but prior to the present invention it has not been possible to use twisted pairs for typical FDDI bandwidths corresponding to transmission speeds in excess of 100 Mb/second.